A 150 m long train crosses a milestone in 15 seconds and a train of same length coming from the opposite direction in 12 seconds. The speed of the other train is?

A. 36 kmph

B. 45 kmph

C. 50 kmph

D. 54 kmph

Answer: Option D

Solution(By Examveda Team)

Speed of first train = $$\frac{{150}}{{15}}$$ m/sec = 10 m/sec
Let the speed of second train be x m/sec
Relative speed = (10 + x) m/sec
∴ $$\frac{{300}}{{10 + {\text{x}}}}$$  = 12
⇒ 300 = 120 + 12x
⇒ 12x = 180
⇒ x = $$\frac{{180}}{{12}}$$ = 15 m/sec
Hence, speed of other train
= $$\left( {15 \times \frac{{18}}{5}} \right)$$  kmph
= 54 kmph